(1) Field of the Invention
The present invention relates to an ice-breaking apparatus for facilitating navigation of ships or barges on icy waters.
(2) Brief Description of the Prior Art
Icebreakers or iceboats have been generally used as vessels navigating on icy waters. In vessels of this type, the kinetic energy of the vessel is utilized for breaking ices and in order to obtain a high ice-breaking capacity, therefore, it is necessary to increase the kinetic energy by enlarging the hull or enhancing the power of the main engine and it also is necessary to improve the structure and shape of the hull per se so that the kinetic energy can be transmitted effectively at high efficiency to ices to be broken. Accordingly, attempts have heretofore been made to attain improvements in the foregoing points. In practice, however, in building ships or vessels of this type, various economical and other limitations are imposed on increse of dimensions of the hull or powering-up of the engine, and therefore, no satisfactory ice-breaking capacity can be obtained in many cases.
In general, the ice-breaking operation is divided in two types; namely, continuous ice breaking applied to relatively thin ices and charging ice-breaking applied to thick ices. Continuous ice breaking is performed by thrust of a ship and a knife edge mounted on the bow. Charging ice breaking is performed by repeating an approach run along a certain distance and a collision against ice.
These conventional ice-breaking methods, however, are very inefficient. For example, in case of continuous ice breaking, the advance speed is ordinarily lower than several knots though the speed is changed to some extent depending on the thickness of ice or the capacity of the ship, and in case of charging ice breaking, the opening distance by one charging operation is only in the range of from several meters to several hundred meters. Accordingly, the ice-breaking efficiency is low, especially in case of charging ice breaking, and further, there is always involved a risk that during the ice-breaking operation, the ship will be blocked by ice and will not be allowed to escape.